With West Coast gasoline prices averaging $4.41 per gallon, even car-crazed southern Californians are joining the nation's slow move away from the automobile and toward public transportation. But even as more Americans pile onto city buses, subways, and suburban trains, the increase at the pump is also hitting transit agencies hard.

"High gas prices are really a double-edge sword," says Virginia Miller, spokeswoman for the American Public Transportation Association (APTA). "While they are bringing more people to ride buses and trains all across the country, public transit agencies are facing challenges to meet their costs."

In many cases this means fare hikes and service cuts. So far this year, nearly half of metropolitan bus operators surveyed by the APTA said they had increased prices to address the strains of rising fuel costs; 19 percent said they had reduced service.

Such fare hikes are hurting the poor disproportionately. While more of the country's suburbanites are choosing mass transit, many of the nation's poorest urban dwellers, whose only option is often public transportation, aren't riding at all because of fare hikes and the downturn in the economy, transportation experts say. Some no longer have a job to commute to, they add.

Los Angeles is in the thick of the quandary. While LA Metro's subways saw a 7.13 percent increase in ridership from April to June compared with a year ago, bus ridership was down 1.9 percent in the same period. Mr. Littman, the Metro spokesman, blamed the drop on a fare hike that raised monthly passes by $10 to $62.

"That fare increase had a huge impact," says Tom Rubin, a Los Angeles-area surface transportation consultant and critic of the LA Metro. "Los Angeles has one of the most transit-dependent riderships in the United States."

As the country's third-largest public-transit network, behind New York and Chicago, respectively, the LA Metro needs to expand faster than it is to meet the demands of a rapidly increasing population, says Littman. "Our dilemma now is to pay for service."

The Metro board's solution: a new tax. It wants to increase the county sales tax by a half penny, a controversial proposal that could go to Los Angeles voters in November.

One of the unresolved questions is how long the surge in mass transit ridership will last. Overall, mass transit ridership climbed 3.4 percent during the first quarter of 2008 compared with the same period last year, according to APTA.

Much of the growth was on commuter lines. There passenger numbers climbed 5.7 percent nationwide during the first quarter compared with a year ago. Ridership jumped 27 percent in Seattle, 17 percent in Harrisburg, Pa., and 10.4 percent in Philadelphia. During the same period, Americans drove 2.3 percent fewer miles, according to the Federal Highway Administration. Last year marked the first such dip since the agency started recording the figure in 1982.

But if the price of oil begins to decline, mass transit ridership could again dwindle, transit experts say.

"We are in uncharted territory," says Robert Poole, director of transportation studies for the Reason Foundation, a free-market-oriented think tank in Los Angeles. "It's too early to tell if we are at a fundamental point of change. The impact is large on transit systems, but small on highway systems."